The Enormous and Distinctive Role of Four-Phonon Scattering in the Thermal Transport Characteristic of Pentagonal Structures

In this paper, the thermal transport characteristics of penta-CN 2 and -BCN, which can be seen as the analogues of penta-graphene, are systematically studied by first-principles calculation and solving the phonon Boltzmann transport equation. The results reveal that, in contrast to the traditional two-dimensional materials, the three-phonon scattering process is insufficient to adequately characterize the thermal transport mechanisms of the above two materials, and the four-phonon scattering process has an enormous impact on their thermal transport processes. The thermal conductivity of penta-CN 2 at room temperature is reduced by 44.1% after considering four-phonon scattering, and that of penta-BCN is dropped by 60.0% in the same case. Combining with phonon analysis, it can be found that four-phonon scattering mainly affects the phonons in the ZA branch, which is mainly due to the extremely isolated distribution of the ZA branch. Further, it can also be noticed that the number of the phonon scattering channel involved in the redistribution process is significantly higher than those of the other two four-phonon scattering processes, i.e., splitting and recombination processes, and even reaches the level of the three-phonon scattering processes. Under the influence of the above factors, the four-phonon scattering process plays an extremely important role in the thermal transport properties of penta-CN 2 and -BCN. Considering that the dispersion curves of the two structures do not have an obvious phonon bandgap, we can notice that the impact mechanism of four-phonon scattering in penta-CN 2 and -BCN is significantly different from those of other structures, which are also greatly affected by four-phonon scattering, e.g., BAs. The results in this work provide strong theoretical support for expanding the application of penta-structures and four-phonon scattering processes in the field of nanoscale heat transfer.